In recent years, there are known internal combustion engines for automotive vehicles employing an in-cylinder injection in which a fuel is directly injected to cylinders, while there are known other internal combustion engines employing the in-cylinder injection as well as an injection of a fuel to intake ports.
The internal combustion engines as described above that wholly or partly employ the aforementioned in-cylinder injection need to pressurize the fuel to be supplied to a fuel injection valve (injector) for in-cylinder injection to a fuel pressure higher than a fuel pressure of an internal combustion engine of port injection type in which the fuel is injected into the intake port, so that the internal combustion engines as described above often use a fuel pump designed to pressurize the fuel pumped from a feed pump by a plunger.
As the fuel pumps of this kind, there are known the fuel pumps comprising a plunger, valve elements, a valve holder and a member forming a fuel passage, the plunger being reciprocatably slidably arranged with respect a pump body (a pump housing), the valve elements being inclusive of a suction valve, a discharge valve and a relief valve and the like, the valve holder being adapted to hold the valve elements.
To be more specific, for example, conventionally known is a fuel pump designed to have a tubular member with a flange pressingly held in an engagement portion between a friction-proof cylinder slidably accommodating a plunger and a pump body, thereby making it possible to have differences in size and thermal expansion between the cylinder and the pump body absorbed in axial and diametric direction or to suppress an erosion of a seal portion caused by pressure propagation from a fuel pressurizing chamber (for example, see Patent Document 1).
Another conventionally known fuel pump is constructed to have an attachment member with a spring mechanism for urging a plunger attached therein and a cover member accommodating a valve body of an electromagnetic valve therein connected by a bolt, so that a cylinder is pressed from the both axial sides while an end portion of a cylinder with a discharge valve and a plunger arranged therein is held in engagement with the valve body, thereby realizing a miniaturization of the fuel pump and reduction of the seal portions (for example, see Patent Document 2).
Still another conventionally known fuel pump is constructed to have a pump housing, in which a valve is arranged, and a cylinder, in which a plunger is accommodated, held in engagement with each other, so that bonding metals are bonded together by diffusion bonding on a tapered bonding surface inclined with respect to an axis line of the cylinder (for example, see Patent Document 3).